This invention relates to a rotor tip clearance apparatus for a gas turbine engine. More particularly but not exclusively this invention relates to a turbine rotor tip clearance apparatus for a gas turbine engine.
Control of clearance variations between gas turbine rotors and their adjacent static structures is essential in the design of efficient gas turbine engines. One area where this is particularly relevant is the gap or seal between a turbine rotor blade and its associated static shroud structure. Centrifugal and thermal loads affect this clearance and various prior solutions have been proposed in order to minimise changes in the clearance.
It is now well known to use active clearance control (A.C.C) to maintain minimum tip clearance throughout use of the engine. One such proposed use of active clearance control is disclosed in our previous patent GB 2 042 646B. This prior invention proposes the use of a plurality of rotatable eccentrics mounted so as to move the annular shroud axially and hence control the clearance between the shroud and rotors. A probe is mounted in an aperture within the engine casing and projects into the clearance thus sensing changes in the size of the clearance (through sensing) pressure changes, which are fed into a control system.
A need has been identified, however for an improved tip clearance control system which is based on the general arrangement disclosed in GB 2042646.
According to the present invention there is provided rotor tip clearance apparatus for a gas turbine engine comprising an annular shroud member being attached to a hollow support ring supported within a guide member, said member having an internal frustoconical face adapted to cooperate with the outer extremities of the rotor to define a clearance therewith, said support ring being controllable so as to alter the clearance between the shroud member and the outer extremities of said rotor wherein said support ring comprises curved portions adapted to cooperate with curved portions in said guide member so as to allow asymmetric movement of said shroud member.